Rituximab anti-CD20 IgG therapy is credited with revitalizing antibody therapies with its ability to effectively treat follicular lymphoma without the extensive side effects associated with more traditional chemotherapy regimens. Since rituximab's approval by the FDA in 1997, the mortality rate from NHL has declined by 2.8% per year (Molina, 2008, Ann Rev Med 59:237-50), and the use of this agent has been expanded to a variety of diseases. While rituximab has been a remarkable success in follicular non-Hodgkin lymphoma (NHL), for which it was first approved, only half of the patients had an objective response, with at most 10% having a complete response (McLaughlin et al., 1998, J Clin Oncol 16:2825-33). Rituximab was less effective in the more aggressive types of NHL, such as diffuse large B cell lymphoma (DLBCL), but when it was combined with combination chemotherapy, improved and durable objective responses compared to the separate therapies were found, making R-CHOP a standard protocol for the treatment of DLBCL (e.g., Leonard et al., 2008, Semin Hematol 45:S11-16; Friedberg et al., 2002, Br J Haematol 117:828-34). The success of rituximab stimulated the evaluation of a number of other antibodies and antibody conjugates, and while a number of these have shown promising activity, to-date only one other unconjugated antibody therapy, alemtuzumab anti-CD52 for chronic lymphocytic leukemia (CLL), has been approved for use in hematologic malignancies (Robak, 2008, Curr Cancer Drug Targets 8:156-71).
The human leukocyte antigen-DR (HLA-DR) is one of three isotypes of the major histocompatibility complex (MHC) class II antigens. HLA-DR is highly expressed on a variety of hematologic malignancies and has been actively pursued for antibody-based lymphoma therapy (Brown et al., 2001, Clin Lymphoma 2:188-90; DeNardo et al., 2005, Clin Cancer Res 11:7075s-9s; Stein et al., 2006, Blood 108:2736-44). Preliminary studies indicate that anti-HLA-DR mAbs are markedly more potent than other naked mAbs of current clinical interest in in vitro and in vivo experiments in lymphomas, leukemias, and multiple myeloma (Stein et al., unpublished results). HLA-DR is also expressed on a subset of normal immune cells, including B cells, monocytes/macrophages, Langerhans cells, dendritic cells, and activated T cells (Dechant et al., 2003, Semin Oncol 30:465-75). Thus, it is perhaps not surprising that infusional toxicities, likely related to complement activation, have been problematic clinically with the administration of anti-HLA-DR antibody (Shi et al., 2002, Leuk Lymphoma 43:1303-12.
A need exists for improved compositions and methods of administration of anti-HLA-DR antibodies or ADCs, alone or in combination with other therapeutic agents, such as kinase inhibitors, for better therapeutic efficacy and decreased systemic toxicity in the treatment of hematopoietic cancers, such as acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL).